Recent data suggests that one of the key biological derangements in the tumor-bearing state is the presence of a continually increasing level of circulating tumor antigen. Because the host responds immunologically, this antigen often circulates as immune complexes. It is possible that this circulating antigen is in some way responsible for the immunologic derangement found in cancer patients. This project proposes to detect the presence of circulating immune complexes in cancer patients, to dissociate those complexes and identify and isolate the antigens. These antigens may prove to be of value for precise diagnostic purposes, and for studies of the biological effects of circulating antigens and antigen-antibody complexes on cell-mediated immune mechanisms and on such things as renal function.